With the continuous improvement of semiconductor technology, image sensor, as a basic information acquisition device in modern society, has been more and more widely used.
Based on the difference in the components used, image sensors can be divided into two categories: charge-coupled device (CCD) image sensors and complementary metal-oxide-semiconductor (CMOS) image sensors. With the development of semiconductor technology, the performance of CMOS transistors is gradually improved, and the resolution of CMOS image sensors becomes to catch up and even surpass the resolution of CCD image sensors. Moreover, CMOS image sensors also demonstrate a number of advanced features, such as high integration degree, small energy consumption, fast speed, low cost, etc.
CMOS image sensor is a typical solid-state image sensor, and is usually formed by an image element array, a row driver, a column driver, a timing control logic, an analog-to-digital (AD) converter, a data bus output interface, a control interface, etc.
Based on the structural difference, CMOS image sensors can be divided into front-side illuminated CMOS image sensors, back-side illuminated CMOS image sensors, and stacked CMOS image sensors. In a front-side illuminated CMOS image sensor, the photodiodes are located behind the circuit transistors, and thus the intensity of incident light may be affected due to the light blocking effect. The relative position of the photodiodes with respect to the circuit transistors in a back-side illuminated CMOS image sensor may be opposite to the relative position of the photodiodes with respect to the circuit transistors in the front-side illuminated CMOS image sensor. That is, the photodiodes in a back-side illuminated CMOS image sensor are located in front of the circuit transistors. Stacked CMOS image sensor is developed from the back-side illuminated CMOS image sensor. Specifically, in a stacked CMOS image sensor, the circuits that are originally arranged right next to the photo-sensitive components are now partially arranged under the photo-sensitive components such that the device may have more internal space. Therefore, in addition to realizing functional diversification, the stacked CMOS image sensor may also achieve the goal for miniaturization.
To increase the intensity of the light, the back-side illuminated CMOS image sensor and the stacked CMOS image sensor allow the light to directly enter the photodiodes without being blocked by other components of the image sensor. Therefore, the quality of the shooting results under a low-light condition may be significantly improved. As such, the back-side illuminated CMOS image sensor and the stacked CMOS image sensor have been widely used in picture-shooting structures in cameras, electronic toys, television conferences, security systems, and other devices.
However, the dark current in conventional CMOS image sensors may be large and the performance of conventional CMOS image sensors may still need to be improved. The disclosed image sensor as well as fabrication and operation methods thereof are directed to solve one or more problems set forth above and other problems in the art.